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Message-ID: <dcc563d10808110620t460b7928hffc2e350f04b9c58@mail.gmail.com>
Date: Mon, 11 Aug 2008 07:20:08 -0600
From: "Scott Marlowe" <scott.marlowe@gmail.com>
To: Henrik <henke@mac.se>
Subject: Re: Filesystem benchmarking for pg 8.3.3 server
Cc: glynastill@yahoo.co.uk, "Greg Smith" <gsmith@gregsmith.com>,
	pgsql-performance@postgresql.org
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References: <158561.15546.qm@web25808.mail.ukl.yahoo.com>
	<D92E27B8-47BF-49FC-A917-947FB44858B9@mac.se>

On Mon, Aug 11, 2008 at 6:08 AM, Henrik <henke@mac.se> wrote:
> 11 aug 2008 kl. 12.35 skrev Glyn Astill:
>
>>>>
>>>>> It feels like there is something fishy going on.
>>>
>>> Maybe the RAID 10
>>>>>
>>>>> implementation on the PERC/6e is crap?
>>>>
>>
>> It's possible.  We had a bunch of perc/5i SAS raid cards in our servers
>> that performed quite well in Raid 5 but were shite in Raid 10.  I switched
>> them out for Adaptec 5808s and saw a massive improvement in Raid 10.
>
> I suspected that. Maybe I should just put the PERC/6 cards in JBOD mode and
> then make a RAID10 with linux  software raid MD?

You can also try making mirror sets with the hardware RAID controller
and then doing SW RAID 0 on top of that.  Since RAID0 requires little
or no CPU overhead, this is a good compromise because the OS has the
least work to do, and the RAID controller is doing what it's probably
pretty good at, mirror sets.